By investing in shares in a public company listed on a stock exchange you get the right to share in the future income and value of that company. Share return can come in two ways:
Dividends paid out of the profits made by the company.
Capital gains made because you're able at some time to sell your shares for more than you paid. Gains may reflect the fact that the company has grown or improved its performance or that the investment community sees that it has improved future prospects.
In some rare cases the capital losses of a company are borne by the shareholders, according to the type of share they have bought.
The price of shares in any individual public listed company can vary from day to day. On any day some shares may go up in value and some down, depending on how investors view the prospects of each company.
Also the listed company shares in a particular country or industry may increase or decrease in price because of rises and falls in economic confidence or changes in the particular industry. There is a range of complex factors which influence share prices on a daily basis and no one can accurately predict what price listed shares will be in the future.